1. Field of Invention
The present invention relates to an end point window assembly in an etching apparatus for fabricating semiconductor devices, more particularly, to a movable spare end point window in an etching apparatus wherein a contaminated end point window is movable so as to be replaced in action by a new window if the spare end point window is sufficiently contaminated by by-products which are generated from reactive rays of plasma gas in a process chamber of the apparatus.
2. Discussion of Related Art
Various methods of etching are used in the fabrication of semiconductor devices. Plasma gas is effective for etching nitride oxide, polycrystalline silicon, and silicon oxide. With plasma gas etchings, an end point detection mechanism for detecting an ending point of an etching process, for informing a worker of the end of etching, and for terminating the etching process is installed in a plasma etch apparatus.
The operational principle of the end point detection mechanism is that each plasma reaction ray generated from the plasma gas has a unique color corresponding to a reaction of the plasma gas with a given film of a process layer on a wafer. Namely, each process layer is clearly identifiable in accordance with colors generated from reactions with each process layer, which are distinguished from one another by spectrum analysis.
Accordingly, in the conventional end point detection mechanism, the etch process is terminated when a unique spectrum corresponding to the last process layer is detected after the spectrums of plasma rays generated from etching the wafer have been analyzed. The end point detection mechanism is connected to a side of a process chamber through a quartz end point window.
FIG. 1 shows an end point detection mechanism according to a conventional art.
Referring to FIG. 1, a wafer is mounted in a process chamber 1. An optic cable 3 transmits plasma reaction rays to a monochromator 5 and is connected to a side of the process chamber 1. An end point window assembly 7 is provided between the process chamber 1 and the optic cable 3 and transmits the plasma reaction rays while blocking passage of reaction by-products. Monochromator 5 analyzes the spectra of the plasma reaction rays and outputs analog signals corresponding thereto. An interface board 9 converts the analog signals into digital signals. The digital signals are then passed to a display 11 where the digital signals are made visible.
The monochromator 5 analyzes the spectra of the plasma reaction rays incident from the optic cable 3 and includes a diffraction grid 13, a motor 15 rotating the diffraction grid 13 in an arbitrary direction, and a photo multiplier tube 17 for converting the values of the spectra reflected by the diffraction grid 13 into analog signals.
FIG. 2 shows the disassembled parts of the conventional end point window assembly.
Referring to FIG. 2, the end point window, through which the plasma reaction rays enter the end point detection mechanism 2, includes an end point bracket 19 connected to the process chamber 1 and having an inducing tube 21 to which the optic cable 3 is connected. A quartz window 23 which blocks passage of the polymers of by-products generated by the etching process lies between the end point bracket 19 and the process chamber 1. An O-ring 25 is positioned inserted around the quartz window 23 and seals a gap between the quartz window 23 and the process chamber 1. A UV filter 27 is installed on the front (exterior side) of the quartz window 23.
The plasma reaction rays enter the conventional end point detection mechanism 2 in the following manner.
Plasma reaction rays, which are generated from the reactions between a given process layer on a wafer and the plasma gas in the process chamber 1, are transmitted to the end point detection mechanism 2 through the end point window assembly 7 and the optic cable 3. More specifically, having been filtered through UV filter 27 and passed through the quartz window 23, the plasma reaction rays are carried to the optic cable 3 connected to the inducing tube 21 of the end point bracket 19.
The plasma reaction rays incident on the end point detection mechanism 2 undergo spectral analysis by way of the monochromator 5 and then are output as analog signals corresponding to the intensity of the plasma.
Such analog signals are converted into digital signals by the interface board 9 in a known manner. Then, the results of the spectral analyses are shown in the display as a picture. Accordingly, the etching process in the process chamber is terminated once the spectrum corresponding to the last process layer on the wafer is detected.
However in the conventional art, polymers generated by the etching process attach to and accumulate on the quartz window and form a byproduct layer. This contaminates the quartz window and prevents the plasma reaction rays from being transmitted by the quartz window, thereby making it difficult to determine the exact end point of etch.
Moreover, frequent disassembly and cleaning is necessary to prevent the polymers from accumulating on the end point window according to the conventional art. This causes a high degree of abrasion of parts and tends to damage the fragile quartz window.